Telephone system



July 26, 1932. v. s. THARP TELEPHONE SYSTEM Inuanh:r U11: DI E. Tharp Filed Jan. 29. 1951 Patented July 26, 1932 UNITED STATES PATENT OFFICE VICTOR S. THARIP, OF EL'MHURST, ILLINOIS, ASSIGNOB, BY MESNE ASSIGNMENTS, 1'0

INC., OF CHICAGO, ILLINOIS, A CORPORA- ASSOCIATEJ) ELECTRIC LABORATORIES,

TION OF DELAWARE TELEPHONE SYSTEM Application filed January 29, .1931.

This invention relates to telephone systems in general and more particularly to telephone systems in which the subscribers lines are classified according to service requirements. The invention is concerned primarily with circuits and apparatus for use in such systems in informing a manual operator of the class to which the line of a calling subscriber belongs.

The problem of identifying subscribers lines in purely manual systems is relatively simple, inasmuch as certain apparatus individual toeach line is within sight of the operator and can, accordingly, be marked in a distinctive manner. In automatic and semiautomatic systems and in manual systems employing automatic call distributing apparatus the operator is called over a common trunking system which necessitates a different type of discriminating arrangement. Under these conditions the use of distinctive tones for identifying calling lines has been found most suitable.

The usual practice when employing tone for discriminating purposes is to arrange the subscribers individual lineswitch (or relay group in case line finders are employed) so that a distinctive tone is applied to the release trunk or holding conductor whenever a call is initiated. With three conductor trunks extending to the switchboard as would ordinarily be the case when the switchboard is located in the same ofiice as the subscribers line equipment, the operator picks up the tone directly from the release trunk conductor as shown in the Martin Patent No. 1,265,225 of May 7, 1918. When the subscribers equipment and the switchboard are located in distant oifices the interconnecting trunks will usually be of the two-conductor type. In this case the trunk repeater is arranged to transfer the tone from the holding conductor of the local trunk to the talking conductors of the inter-oflice trunk. This tone may be applied to the inter-ofiice trunk immediately on its seizure by the calling subscriber, or under control of the operator after the call is answered. It has been the practice in the past to provide a key associated either with the trunk or with the operators cord circuit for Serial No. 512,047.

removing the tone from the trunk in the first instance, or for causing the repeater to apply the tone to the trunk in the second instance. These two arrangements are shown, respectively, in the V. S. Thar and T. F. Crocker Patent N 0. 1,792,452 of eb. 10, 1931, and 1n the Martin Patent No. 1,693,613 of December 4, 1928. In either case additional keys at the operators-position are required and 1f existing trunks and cord circuits are to be used they must be modified accordingly. Furthermore, the key operation imposes additional duties on the operator which tend to slow up the service.

The arrangement contemplated in the present invention is similar to that shown in Patent N 0. 1,7 92,452, previously referred to, in that the toneis applied to the talking conductors of the trunk on seizure, and is removed after the call has been answered and the tone heard by the operator. The present arrangement, however. overcomes the objectionable features of the prior systems by dispensing with the special tone control keys and making this control entirely automatic. The tone,-as stated, is applied to the talking conductors of the trunk on seizure and will be audible to the operator immediately on answering the call. The act of answering initiates the operation of a slowacting relay device which, after a predetermined interval, automatically removes the tone from the trunk line without further action on the part of the operator.

The various features of the invention together with the operation of a telephone system embodying the same will be described in detail hereinafter, reference being had to the I accompanying single sheet of drawing. The application of the invention to an automatic telephone system has been shown by way of example. It will be appreciated that the invention may be applied as readily to semiautomatic systems and to manual systems employing automatic call distribution.

Referring now to the drawing there is shown a subscribers line and substation T with the associated individual lineswitch' finder arranged to apply discriminating tone to the release trunk or holding con uctor will serve equally well. The line of substation T is one of a group of lines of a class identified by tone from the tone generator TG. Lines of other classes will be similarly marked by tone from other tone generators, such as the enerator TG'. Lineswitch LS, together wit other similar lineswitches has access to the usual'selector switches of which selector S, shown only in skeleton form, is one. The selector has access over certain levels of its bank to local switches (not shown) of the automatic exchange and over other levels to trunks extending to a manual switchboard. The automatic to manual trunk shown terminates in repeater R at the automatic exchange and in jack J at the switchboard. Calls over the trunk are answered by means of cord circuits of which one, cord 0', is shown in part. The cord circuits may be of any suitable type commonly provided for manual or toll service. Cords of the type which connect up the operators telephone set automatically, such as that shown in Patent No. 1,802,449, granted April 28, 1931, to A. W. Steinke, are particularly suitable although those employing a key for this purpose will operate satisfactorily.

The operations involved in the extension of a call from substation T to the switchboard will now be described in detail to more fully explain the various features of the invention. Upon the initiation of a call at substation T, a 100 circuit is closed over which line relay 5 0 the lineswitch operates. Relay 5 completes the stepping and test circuit so that, if necessary, the switch wipers may be advanced step-by-step until an idle trunk is found. It may be assumed that the trunk comprising conductors 19'21 is the "wipers 16 and 18 to the line rela first idle trunk found by the lineswitch and. that the trunk is taken into use upon the operation of switching relay 4 of the lineswitch. The calling subscribers loop is thereby extended over contacts 8 and .11 and of the selector S. The selectoris prepare for operation in the usual way and ground is returned over release trunk conductor 20 to maintain switching relay 4 operated after slow-releasing line relay 5 restores. The calling subscriber now dials the digit assigned for callin the manual exchange and wipers 22-24 of the selector are ra'med to the level in which the automatic to manual trunks are accessible. The selector rotates in the usual manner to select an idle trunk, which for convenience will be assumed to be the trunk comprising conductors 2527 which terminates in repeater R. The calling subscribers loop is further extended over wipers 22 and 24 of the selector, conductors 25 and 27 of the seized local trunk, contacts 37, and 42, upper and lower windings of relay 28 to battery and ground,1 respectively.

trunk conductor 26 by way of contacts 44 and the lower winding of the tone transformer 32, to ground. This ground serves to hold the switching relays of selector S and lineswitch LS. in the usual way. Relay 30 also completes a circuit which may be traced from ground, contacts 45, thence over two parallel branches, one of which includes contacts 57 and relay 34, the other including contacts and relay 33. Relay 33 operates and connects the generator GEN and ground across the outgoing trunk at contacts 51 and 48, completes a locking circuit for itself at contacts 49 and connects ring-back-tone to the lower talking conductor of the repeater at contacts 50. Relay 34 energizes but its contacts 52 are not closed immediately, due to the vibration of the armature spring to which the weight 88 is attached. Ringing current from the generator GEN by way of contacts 51 and 62, trunk conductor 64, contacts 73, upper winding of relay 65, condenser 67, contacts 72, trunk conductor 63, contacts 53 and 48 to ground, energizes relay 65. This relay on operating completes a circuit for its lower winding by way of contacts 69 and 74, and at contacts 68 completes a circuit for the busy visual signal 75 and lamp L in parallel. Si nal 75 operates to mark the trunk busy at t e various positions of the switchboard and lamp L lights to notify the operator of the call. Referring back to the repeater, rin ing current is a plied over the circuit a ove traced until the springs of relay 34 come to rest and contacts 52 close whereon the ground by way of contacts 45 is extended over contacts 52 and to relay 35. Relay 35 operates, disconnects the generator and ground from the trunk at. contacts 62 and 53, and at contacts 61 and 54 extends the trunk conductors through to the windings of relay 29. Relay 35 opens the original energizing circuit of relay 33 at contacts 55, completes a holding circuit for itself at contact 56, opens the original energizing circuit of relay 34 at contacts 57, and prepares a new energizing circuit for that relay at contacts 58. Relay 34 accordingly restores and relays 33 and 35 remain energized over the locking circuits completed on their operation. During this time ring-back-tone by way of contacts 50, lower-talking conductor and condenser of the repeater, contacts 37 and trunk conductor 25 and the upper-talking conductor of the selector and lineswitch will inform the calling subscriber that the operator is being signalled.

On noting the lighted condition of lamp L the operator will answer the call by inserting the plug P of the cord G into the jack J, thereby com leting a circuit which may be traced from attery, winding of rela 76, resistance 89, sleeve contacts of the u and jack, winding of relay 66, to ground. Itelay 76 operates and shunts resistance 89 at contacts 81, thereby permitting relay 66 to operate. Relay 76, among other things, prepares the supervisory circuit at contacts 79 and pre ares a circuit for relay 78 at contacts 80. elay 66 opens the circuit of lamp L at contacts 70, completes a local-circuit for the busy visual slgnal 75 at contacts 71, disconnects the upper winding of relay from trunk conductors at contacts 72 and 73, and opens the circuit of the lower winding of that relay at contacts 74. A circuit can now be traced from battery, upper winding of relay 77 of the cord circuit, tip contacts of the plug and jack, trunk conductor 63, contacts 54 and operated reversing contacts of relay' 28, lower winding of relay 29, upper winding of tone transformer 32 to ground, and from round through the lower winding of relay 7 ring contacts of the plug and jack, trunk conductor 64, contacts 61, operated reversing contacts of relay 28, upper winding of relay 29 to battery. Both relays 29 and 77 operate over the above circuit. Relay 77 completes a circuit at contacts 83 for relay 78, which operates and connects the operators telephone set 'across the talking strands of the cord at contacts 85 and 86. Relay 29 reverses the connection of relay 28 to trunk conductors 25 and 27 by opening contacts 37 and 42 and closing contacts 38 and 43. An additional circuit is closed for relay 30 at contacts 41 and a circuit is completed by way of ground, contacts 45, 40, and 58 for relay 34. As before stated relay 34 energizes but, due to its weighted armature spring, does not close contacts 52 for an appreciableinterval thereafter. During this interval tone from the tone generator TG is transmitted over the battery feed conductor of the lineswitch, winding of magnet 6, contacts 15, winding of relay 4, contacts 10, wiper 17, conductor 20, wiper 23, conductor 26, contacts 44, lower winding of tone transformer 32 to ground. This tone is induced in the upper winding of transformer 32, which'as stated is connected in series with the lower winding of relay 29. The tone is thus applied to the talking conductors of the inter-ofiice trunk and is audible to the operator who is thus advised of the class of the line originating the call. When the vibrating springs of relay 34 come to rest after an interval ground is extended over contacts 52 and 59 to slow-operating relay 31. This relay operates after a slight delay and short-circuits the upper and lower windings of transformer 32 at contacts 46 and 47, thereby removing the tone from the talking conductors of the inter-ofiice trunk. It w1ll be seen that the application of tone to the trunk and its removal therefrom is accomplished automatically responsive to the operator plugging into the ack. The operator may now converse with the calling subscriber and complete the call or deny service as re uired under the circumstances. In case t e o rator should desire to verlfy the class 0 the line, it is only necessary to momentarily withdraw the plu again from the jack. The previously trac clrcuit of relay 29 will be opened and that relay will restore. Relay 29, of course, opens the circuit previously traced for relays 34 and 31, and those relays restore. Upon reinserting the plug into the jack, relays 29, T

34, and 31 are reoperated in the same manner as when the call is first answered and the tone is momentarily applied to the interoflice trunk.

When the calling subscriber hangs up at the end of the conversation, relay 28 restores and again reverses the connection of relay 29 to the talking conductors of the inter-oflice trunk. The windings of relays 29 and 77 are now connected in opposition and the relays deenergize. Relay 29 opens the circuit of relay 30 which releases and permits the precedin switches to restore in the usual manner. elay 77 on releasing, completes a circuit at contacts 82 for supervisory lamp L1. This lamp glows to indicate to the operator that the calling subscriber has hung up whereon the operator removes the plug P from the jack. Upon removal of the plug, relay 66 restores and again connects relay 65 across the trunk in readiness to receive the next call.

What is claimed is:

1. In a telephone system, a subscribers line identified by a distinctive tone, a trunk line, means for extending a call from said subscribers line to the trunk line, means for applying said tone to the trunk line,- means for answering the call, and means responsive to the answering of the call for removing said tone from the trunk line after a predetermined interval.

2. In a telephone system, a subscribers line, a source of tone associated with said line, a trunk line, means for extending a call from said subscribers line to the trunk line, means for connecting said tone source to the trunk line responsiveto the call, means for answering the call, and means automatically operative a predetermined interval after the call is answered for disabling said tone source.

3. In a telephone system, a subscribers line identified by a distinctive tone, a trunk line, means responsive to a call from said subscribersline to said trunk line for applying said tone the trunk line, means for answering the call, slow operating means for removing said tone from the trunk line, and means responsive to the answerin of a call for initiating the operation of said last means.

4. In a telephone system, a subscribers line identified by a distinctive tone, a trunk line, means responsive to a call from said subscribers line to said trunk line for applying said tone to the trunk line, means for answering the call, a first slow-operating rela associated with the trunk ine operate responsive to the answering of the call, and a second slow-operating relay controlled by 1.- ssaid first relay for removing said tone from the trunk line.

5. In a telephone system, a trunk line comprising two talking conductors connecting two exchanges, a test conductor for the trunk at one exchange, means for applying a distinctive tone to said test conductor when a call-is extended over the trunk line from said one exchange, means for transferring said tone from said test conductor to the talking conductors of the trunk line, and means responsive to the answerin of this call for removing the tone from sai talking conductors after a predetermined interval.

6. In a telephone system, a trunk line comprising two talking conductors connecting an automatic exchange and a manual switchboard, a test conductor for the trunk at the automatic exchange, means responsive to the extension of a call from the automatic exchange to the switchboard via said trunk line for applying a distinctive tone to said test conductor, a transformer for transferring the tone from said test conductor to the talking conductors of the trunk, 'and means operated responsive to the answering of the call for shunting said transformer after a predetermined interval to remove the tone from said talking conductors.

7. In a telephone system, a trunk line, means for applying a distinctive tone to the trunk line responsive to a call thereover, means for answering the call, a slow operating means for removing said tone from the trunk line, and means responsive to the answering of the call for inltiating the operation of said last means.

8. In a telephone system, a trunk line comprising two talking conductors and a test conductor, an induction 'coil, means responsive to the extension of a call to the trunk line for inductively connecting said test conductor and one of said talking conductors through said coil, means for answering the call, and means automatically operative responsive to the answering of the call for short-circuiting said coil after a predetermined interval of time.

9. In a telephone system, a trunk line, a

double wound induction coil, two talking conductors for the trunk line, one of which extends through one winding of said coil, a test conductor for the trunk line, means respon: sive to the extension of a call to the trunk line for extending said test conductor throu h the other windin of said coil, means or answering the ca slow operating means for short-circuiting the windings of said coil, and means responslve to the answering of the call for initiating the operation of said last means.

10. In a telephone system, lines of two classes, a trunk line, means for extending a call from a line ofeither class over the trunk line, means for answering the call, means responsive to the extension of a call for applying a distinctive signalling current to the trunk line, and means operated responsive to the answering of the call for removing said signalling current from the trunk line after a delay of a predetermined interval.

11. In a telephone system, lines of two classes, a trunk line, an answering circuit, means for connecting a line of either class to one end of the trunk line, means responsive to said connection for applying a dis tinctive signalling current to the trunk line, means for connecting said circuit to the other end of the trunk line, means responsive to said last connection for initiating the operation of a slow-acting device to automatically remove the signalling current from the trunk line, and means responsive to the termination of said last connection for reapplying the signalling current to the trunk line.

12. In a tele hone system, a trunk line comprising two tal ing conductors and a test conductor, a second trunk line comprising two talking conductors, a repeater connecting said trunk lines, a transformer in the repeater inductively connecting the test conductor of said first trunk line with a talking conductor of the second trunk line, a slow-operating device in the repeater, means controlled over the second trunk line for initiating the operation of said device, and means controlled by said device upon the. completion of its operation for short circuiting said transformer.

In witness whereof, I hereunto subscribe my name this 26th day of January, A. D.

VICTOR S. THARP. 

